FAULT DIAGNOSIS METHOD FOR INJECTORS OF INTERNAL COMBUSTION ENGINE HIGH-PRESSURE INJECTION SYSTEMS

Abstract: A method consisting in successively supplying the injector coils (L1, L2) for a predetermined time by closing the respective switch (S1, S2); discharging the supplied coil into a storage capacitor (12); measuring the charge of the storage capacitor following discharge of the coil; and comparing the measured charge value with a predetermined threshold. A short-circuit test is first performed by supplying each coil for a very short time interval, to prevent the current flow from damaging the control circuit (1) in the event of short-circuiting, and by determining the measured charge is below a first threshold. Subsequently, an open-circuit test is performed by supplying each coil for a longer time interval, and by determining the measured charge is above a second threshold.

Description: FAULT DIAGNOSIS METHOD FOR INJECTORS OF INTERNAL COMBUSTION ENGINE HIGH-PRESSURE INJECTION SYSTEMS TECHNICAL FIELD The present invention relates to a fault diagnosis method for the injectors of internal combustion engine high-pressure injection systems, in particular for detecting short-circuiting or open circuits on the injector coils. BACKGROUND ART As is known, high-pressure injection systems comprise a number of injectors, opening and closing of which are controlled by means of a respective coil and a control circuit. Any short-circuiting or open circuits on the coil must therefore be detected immediately to ensure correct operation of the injector and also prevent damage to the injector, control circuit. This applies in particular to short-circuiting of the injector, which, if not detected immediately, may result in such high currents as to irreparably damage the electronic components of the control circuit. DISCLOSURE OF INVENTION It is an object of the present invention to provide a straightforward, reliable method of diagnosing short-circuiting and open circuits on injectors. According to the present invention, there is provided a fault diagnosis method for the injectors of internal combustion engine high-pressure injection systems, 'characterized in that it comprises the steps of: supplying an injector coil for a predetermined time; discharging said coil into a storage capacitor; measuring the charge of said storage capacitor; and comparing said charge with a predetermined threshold. BRIEF DESCRIPTION OF DRAWINGS A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows an electric diagram of the circuit controlling the injectors of a high-pressure electronic injection system; Figure 2 shows graphs of a number of electrical quantities measured in the Figure 1 circuit using the method according to the present invention and relative to the absence and presence of short-circuiting on the injector coil; Figure 3 shows graphs of a number of electrical quantities measured in the Figure 1 circuit and relative to the absence and presence of an open circuit; Figure 4 shows a flow chart illustrating the steps in one embodiment of the method according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION Figure 1 shows a simplified diagram of the circuit 1 for controlling a number of injectors. Circuit 1 comprises a number of actuator circuits M. , M_, ... connected parallel to one another between a supply line 4 and a ςfround line 5, and each comprising, in series, a coil L , L_, ... for controlling a respective injector, a twisted ca_ble C , C , ... of appropriate length, and a controlled switch S. , S_, ... . A voltage source 7 is also connected, via a decoupling diode 8, between supply line 4 and ground line 5. - - The common node N , N_, ... between each coil L_, L_, ... and each controlled switch S. , S„, ... is connected to a terminal 11 of a storage or tank capacitor 12 via a respective decoupling diode D-, D_, ... with its cathode connected to terminal 11; and terminal 11 is connected to supply line 4 via a controlled switch 14. The method according to the present invention is performed during startup, as soon as the ignition key is turned, to prevent the engine from being started up in the event of a fault which may impair operation or even cause irreparable damage to the component parts of control circuit 1. The method consists in briefly and successively turning on the controlled switches of the coils to connect the switches successively to the battery. At this step, if the coil is connected properly, the current through the supplied actuator circuit is low (due to the short connection time) , and is high in the event of short-circuiting of the coil. When the controlled switch is turned off, the current from the previously supplied actuator circuit is transferred to storage capacitor 12 which therefore charges to a voltage depending on the amount of current transferred, which in turn is related to the current through the previously supplied actuator circuit. In the event of short-circuiting, the capacitor charges to a much higher voltage as compared with a properly connected coil, so that short-circuiting may be detected by calculating the voltage increase of the capacitor and comparing it with a threshold value. The above behaviour patterns are shown in Figure 2, which shows a graph of the current through the injector circuit and a corresponding graph of the capacitor voltage in the event of correct connection (curves A, B) and short-circuiting ' (curves C, D) of the coil. After all the coils in the circuit have been short-circuit tested (with no fault being detected on any of the coils) , a check is made to determine the presence of open circuits, for which purpose, the controlled switches of the coils are turned on successively, as for short-circuit testing, but for a greater length of time. In the event of an open circuit on the coil, no current flows through the coil, so that, when the respective controlled switch is turned off, no current is transferred to charge capacitor 12. In this case also, therefore, correct or incorrect connection of the injector coils may be detected by measuring the voltage increase of the capacitor. Figure 3 shows graphs of the voltage of storage capacitor 12 in the event of an open circuit on a coil (curve E) and correct connection of all the coils (curve F relative to a different supply voltage value) . In this test, storage capacitor 12 is discharged after each coil is tested, for better indicating, each time," the charge of the capacitor, the final value of which depends on various parameters, including the initial voltage prior to current transfer. One embodiment will now be described with reference to Figure 4. To begin with, block 20 measures the voltage V(0) of capacitor 12; block 21 sets an injector counter i. to i; and block 22 closes switch S. for a very short time Tl, e.g. from 3 to 30 μs, which time must be long enough to permit current flow, but short enough to prevent damaging the controlled switch in the event of short-circuiting (in which case, the current may reach a few tens of Amps) . Block 23 then measures the voltage V(i) of the capacitor; block 24 calculates the difference DV1 = V(i) - V(i-l) ; and block 25 compares voltage difference DV1 with a threshold Kl. If DV1 exceeds threshold Kl, block 26 generates an error signal to prevent startup of the engine. Conversely, if DV1 is below threshold Kl, block 27 increments the counter; and block 28 determines whether all the injectors have been tested. If they have not, block 28 goes back to block 22; if they have, block 28 goes on to block 30. Block 30 initializes two injector and fault (open circuit) counters i. and j; block 31 discharges capacitor 12 (e.g. by closing switch 14 until capacitor 12 reaches the voltage of source 7) ; block 32 measures the voltage V(0) of the discharged capacitor 12; block 33 turns on switch S. for a time T2, e.g. from 70 to 200 μs; block 34 measures the voltage V(i) of capacitor 12; block 35 calculates the difference DV2 = V(i) - V(0) ; and block 36 compares the voltage difference with a threshold K2. If DV2 is above threshold K2, block 36 goes on to block 37 which increments counter i, and to block 38 which determines whether all the injectors have been tested. if they have, the procedure is terminated. If they have not, block 38 goes back to block 31. Conversely, if DV2 is below threshold K2, block 36 goes on to block 41 which increments the fault counter j; block 42 generates a signal indicating an open circuit on the i-th coil; and block 43 determines whether it is the first open circuit to be detected. If it is, block 43 goes back to block 37. Conversely, if a second open circuit is detected (j = 2) , block 43 goes on to block 44 which signals an open circuit on the second coil, so that the diagnostic control system disables startup of the engine. The method described therefore provides for indicating any faults without damaging the control circuit, by first performing the short-circuit test indicating the more hazardous condition and which, by virtue of the very short length of time the switches are closed, poses no risk to the circuit, and by subsequently performing the open-circuit test which may thus be performed in the most appropriate" manner by closing the controlled switches for a greater length of time to allow a greater current flow and so indicate any open circuits with no danger of damaging the circuit. Moreover, the method according to the present invention is straightforward and reliable, and may be program implemented with no complex, high-cost alterations to the circuitry. Clearly, changes may be made to the method as described and illustrated herein without, however, departing from the scope of the present invention.

Claims: CLAIMS 1) A fault diagnosis method for the injectors of internal combustion engine high-pressure injection systems, characterized in that it comprises the steps of: supplying an injector coil (L. , !_ ) for a predetermined time; discharging said coil into a storage capacitor (12) ; measuring the charge of said storage capacitor; , and comparing said charge with a predetermined threshold. 2) A method as claimed in Claim 1, characterized in that it comprises the step of -determining short-circuiting of said injector coil (L. , L_) and wherein said coil is supplied for a first very short time interval (Tl) . 3) A method as claimed in Claim 2, characterized in that said first time interval ranges from 3 to 30 μs. 4) A method as claimed in Claim 2 or 3, characterized in that said step of determining short-circuiting of said injector coil (L., L_) is followed by the step of determining the presence of open circuits and wherein said coil is supplied for a second time interval (T2) greater than said first time interval (Tl) . 5) A method as claimed in Claim 4, characterized in that said second time interval ranges from 50 to 200 μs. 6) A method as claimed in any one of the foregoing Claims, characterized in that said step of measuring said charge comprises the step of determining the voltage increase of said storage capacitor (12) as said coil (L-, L 2 ) is discharged. 7) A method as claimed in Claim 6, characterized in that, to determine short-circuiting of said injector coil (L-v L 2 ) * said step of determining said voltage increase comprises the step of memorizing the charge value of sa;Ld capacitor (12) immediately prior to said step of supplying said coil; measuring the voltage of said capacitor after said charging step; and determining the difference between said memorized charge value and said measured voltage. 8) A method as claimed in Claim 6, characterized in that, to determine the presence of open circuits on said injector coil (L 1 , L_) , said step of determining said voltage increase comprises the step of discharging said capacitor (12) immediately prior to said step of supplying said coil; memorizing the discharge value of said capacitor; measuring the voltage of said capacitor after said charging step; and determining the difference between said memorized discharge value and said measured voltage. 9) A method as claimed in any one of the foregoing Claims, characterized in that, in the event a short-circuit is detected, a signal is generated to prevent startup of the engine. 10) A method as claimed in any one of the foregoing Claims, characterized in that, in the event more than one open circuit is detected, a signal is generated to prevent startup of the engine. 11) A fault diagnosis method for the injectors of internal combustion engine high-pressure injection systems, substantially as described and illustrated herein with reference to the accompanying drawings.

Inventors: BORTIGNON GIORGIO, GROPPO RICCARDO, TUBETTI PAOLO, BORTIGNON, GIORGIO, GROPPO, RICCARDO, TUBETTI, PAOLO
Applicants: BORTIGNON GIORGIO, BOSCH GMBH ROBERT, GROPPO RICCARDO, TUBETTI PAOLO, BORTIGNON, GIORGIO, GROPPO, RICCARDO, ROBERT BOSCH GMBH, TUBETTI, PAOLO
Application year: 1994
Main classification: F02D41
IPC codes: F02D41, F02D45, F02M65